1. Field of the Invention
The present invention relates to a novel hydrophilic polymer which has a terminal silane coupling group and is utilizable in applications such as antifogging paints, exterior antifouling paints, and in a hydrophilic layer for a lithographic printing plate base.
The present invention also relates to a lithographic printing plate base having a novel hydrophilic layer. More particularly, the invention relates to a lithographic printing plate base which, when used as a lithographic printing plate precursor, can have high hydrophilicity without a sacrifice of film strength.
2. Description of the Invention
Although various hydrophilic polymers have hitherto been known, no hydrophilic polymer having a silane coupling group at a terminal is known. This hydrophilic polymer is useful because it is widely utilizable in applications including antifogging paints and exterior antifouling paints.
The hydrophilic bases or hydrophilic layers which have hitherto been used in lithographic printing plates include an anodized aluminum base and a base or hydrophilic layer obtained by treating the anodized aluminum base with a primer, such as a silicate, poly(vinylphosphonic acid) (see Japanese Patent Laid-Open No. 1853/1995), or poly(vinylbenzoic acid), for further enhancing hydrophilicity. Investigations on such hydrophilized aluminum bases and hydrophilic layers are being made enthusiastically. Furthermore, a technique of using a polymer having sulfo groups in forming an undercoat layer for a photosensitive layer is described in Japanese Patent Laid-Open No. 101651/1984.
On the other hand, techniques concerning hydrophilic layers not for metallic supports such as aluminum supports but for flexible supports such as PET (poly(ethylene terephthalate)) or cellulose acetate supports are known. Examples of such hydrophilic layers include: the hydrophilic layer disclosed in Japanese Patent Laid-Open No. 292558/1996 which comprises a hydrophilic polymer and a hydrophobic polymer and is capable of swelling; the PET support disclosed in EP 0709228 which has a microporous hydrophilic crosslinked silicate surface; and the hydrophilic layer disclosed in Japanese Patent Laid-Open Nos. 272087/1996 and 507727/1996 which comprises a hydrophilic polymer and has been cured with a tetraalkylorthosilicate hydrolyzate.
The formation of those hydrophilic layers gives lithographic printing plates which yield satisfactory printed matters and are less apt to cause scumming (stain) in the initial stage of printing. However, from the standpoint of higher suitability for practical use, there has been a desire for a lithographic printing plate precursor which has a hydrophilic layer having higher hydrophilicity and not peeling off the support even under severer printing conditions and which gives printed matters free from scumming. Although it has been known that a hydrophilic layer can be made to have higher hydrophilicity by increasing the water-holding capacity of the hydrophilic layer, this technique arouses the following problem. In case where hydrophilic layers according to the related art are modified so as to heighten the water-holding capacity thereof, the hydrophilic layers thus obtained have enhanced swelling properties and, hence, a weakened film structure and reduced strength or have imparted adhesion to the support.